Primary frequency control by wind turbines

The speed of modern converter controlled wind turbines is almost completely decoupled from the grid frequency. Accordingly, wind turbines do not possess a natural response to frequency excursions. In this paper three different control concepts that enable wind turbines to participate on grid frequency control are introduced. The first uses pitch control together with the provision of reserve capacity by operating the wind turbine in part load mode. The second and third strategies utilize the kinetic energy of wind turbines to provide frequency support for a limited time following a disturbance. One involves a control scheme which initiates the partial release of the kinetic energy immediately after the frequency drop is detected. Replenishing the stored energy and thus accelerating the wind turbine then follows during the frequency recovery phase. The third option calls for the wind turbine to accelerate first, and then decelerate by discharging energy during the phase of the disturbance in which the frequency is approaching its minimum, thus limiting the frequency drop more effectively. For all three concepts the control structures are presented, and the effectiveness of the suggested methods is demonstrated using simulation results.